MMP9 and infectious disease: MMP-9 has been demonstrated to regulate leukocyte function through a number of mechanisms, including activation of pro-IL-1β into IL-1β and truncation of IL-8 into a more active form and, as degranulation of MMP-9 from neutrophils is stimulated by IL-8, thus creating a positive feedback loop.[42] MMP-9 may therefore potentially play a role in the course of infectious diseases; and possibly in pulmonary disease.